Posted: Sun Nov 08, 2009 1:16pm

I have recently bought a Narrowboat for leisure use and am concerned about how best to keep the batteries charged during the winter period when I will only be using the boat about one weekend a month. It has 3 domestic batteries and one starter, plus a small solar panel. Is it sensible to leave the solar panel permanently connected to trickle charge, or will I need to take the batteries out periodically and use a mains battery charger?

Posted: Sun Nov 08, 2009 3:18pm

Dear Richard, without details about the domestic bank size, the panel output and if you have a charge controller or not it is difficult to give you a definitive answer. I will assume that your three domestic batteries equates to a bank of 330Ah and this means you can couple a solar panel of up to 30 watts directly to the bank without a regulator. Now, if the panel is a £20 Maplin special then it has a 1.5 Watt output. With the panel at 90 degrees to the sun it will produce about 0.1 (one tenth) of an amp. I doubt you will have it at 90 degrees to the sun and tracking it so in reality it will be far less than this. Lead acid batteries discharge at between 8% & 40% per month so lets say 20%. This means your domestic bank will discharge by 66Ah per month yet the solar panel will produce less than 24 Ah during a winter month with no clouds. Then you have to consider that you need to put back up to 40% more electricity than went out. based on these assumptions I would advise that you use the solar panel to charge the engine battery and make sure that when you are using the boat that you run the engine at charging speed for 5 hours or so. If you can easily take the batteries home for charging so much the better. This will go some way towards minimising sulphation and prolonging battery life. Please remember all this is based on assumptions about what you have. If I am wrong please come back with more information. Tony Brooks

Posted: Wed Nov 11, 2009 9:19am

Thanks for your advice. Your assumptions seem about right, although I cant confirm all the details as I haven’t yet completed purchase of the boat and it is moored some distance away. One further question if I may – If I have a 240v shore connection available and a portable battery charger, is it OK to use that to charge the domestic battery bank as a whole without disconnecting the battery connections? Regards, Richard Drage

Posted: Wed Nov 11, 2009 9:51am

If it is a modern unit that reduces the voltage when it thinks the battery is charged it should be fine. However typically they deliver a maximum of 8 amps so your 330Ah bank could take a long time to charge. This is no bad thing in the later stages but it would involve leaving the charger connected for possibly several days and I would not be over keen to leave a car charger working whilst unattended. Personally I would rather you bought a proper marine multi-stage charger and left it connected to the shoreline when you are away from the boat. Tony Brooks

Posted: Wed Nov 11, 2009 3:50pm

I see you have received similar advice both here and in the other place and both concur save in one point. The research I was sable to carry out on the net and elsewhere does not lead me to believe there is a device that will reverse sulphation in all cases so can not recommend spending money on such a device - far better put that money towards a decent solar cell or battery charger. TB